A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of one, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In case of an interior space of the apparatus, for example a vacuum space, it is generally desired to monitor the interior space for contamination. This is the case, for example, when the interior space is used in a lithographic process, or, for instance, when the space is included in a lithographic apparatus. In that case, it is desired to detect contamination quickly—preferably within a fraction of a second—so that a lithographic process can be halted immediately, to prevent contamination sensitive optics being spoiled by the contamination. For example, the lithographic process can be halted by stopping the exposure, by stopping a radiation source and/or by closing a shutter in the path of the radiation beam. However, the interior space can also be applied in different fields, for instance general semiconductor industry, general vacuum technology industry, space technology and the-like. The present invention can therefore also explicitly be applied outside the field of lithography.
United States Patent Application Publication No. 2002/0083409 A1 relates to EUV lithography devices and processes, wherein a quartz crystal microwave is use as a measuring device.
European Patent Application Publication No. EP 1 452 851 A1 relates to a method and device for measuring contamination of a surface of a component of a lithographic apparatus. The measuring device has a radiation transmitter device for projection radiation on at least a part of said surface and a radiation receiver device for receiving radiation from the component.